1. Field of the Invention
The present invention relates to an optical disk for an optical disk player, and more particularly, to an optical disk having a pattern which allows detection of degree of a tilt of disk.
2. Description of the Related Art
In a compact disk player or a digital video disk player, the tilt of a disk is a major factor in deteriorating reproduction of a signal. In particular, as the aperture ratio of an objective lens increases with increased density of a recording medium and the wavelength of a laser beam decreases, deterioration in performance due to the tilt becomes much greater. Accordingly, it is very important to correct the deteriorated performance due to the tilt of a disk having a high density recording medium.
To correct signal deterioration due to a tilt of a disk in an optical disk player, a shaft of a spindle motor is inclined, or a deck for installing a disk or optical pickup mechanisms for detecting a signal is inclined. For correction, it should be determined to what degree and in which direction a disk is inclined at the initial stage of disk reproduction.
A conventional tilt detection apparatus is shown in FIG. 1 and disclosed in U.S. Pat. No. 4,829,508. In the above tilt detection apparatus, an optical signal emitted from a light emitting diode 1 is projected to a disk 4 and the optical signal reflected by the disk 4 is received by two light receiving diodes 2 and 3, to thereby detect the degree of tilt of a disk. That is, in the structure shown in FIG. 1, if the disk 4 is not tilted, the amplitudes of optical signals detected by the two light receiving diodes 2 and 3 are substantially the same. When the disk 4 is tilted, the amplitudes of optical signals detected by the two light receiving diodes 2 and 3 are different according to the degree of tilt. The degree of tilt is detected by a differential amplifier 5 for detecting the difference between the optical signals detected by the two light receiving diodes 2 and 3. Here, the light emitting diode 1 and the light receiving diodes 2 and 3 are represented in the form of a photo-coupler 6.
The conventional tilt detection apparatus having the above structure requires an additional optical mechanism, such as a photo-coupler, for detecting the degree of tilt. Also, an additional signal processing portion for detecting the tilt of a disk is needed. Further, since an offset of a detected signal according to the initial state of a mechanical structure and disk assembly is present, the degree of detection of a signal deteriorates.